西昆仑库地蛇绿岩的成因及构造意义

库地蛇绿岩位于康西瓦大型走滑断裂带的北侧,主要由裂解的变质橄榄岩,堆晶岩和块状枕状玄武岩组成,其上覆岩石为杂色火山碎屑岩和具浊流沉积的碎屑岩系。前人对库地蛇绿岩已作过较系统的报道1]。震旦纪-早奥陶纪为本区蛇绿岩的洋盆发育时代,其侵位可能代表了晚元古代到早古生代的重要板块运动的记录。本文通过变质橄榄岩的矿物学、熔岩的地球化学等研究,表明库地蛇绿岩经历了洋中脊(MOR)到俯冲带(SSZ)的构造环境转变过程,致使地幔橄榄岩达到~30%的部分熔融程度。

Genesis and tectonic significance of the Kuda ophiolites in western Kunlun Mountains, Xinjiang

The Kuda ophiolites hosted on the northern side of the Kangxiwar strike-slip fault in western Kunlun Mountains, Xinjiang are made up of dismembered metamorphic peridotites, cumulate rocks and massive pillow basalts, and overlain by the variegated pyroclastic rocks and clastic rocks with turbidites. The Sinian to Early Ordovician is interpreted as the major periods for the formation of the oceanic basin for the Kuda ophiolites, and the emplacement of the ophiolites may represent the important records for the plate motion in the study area during the Late Proterozoic to the Early Palaeozoic. The chemical characteristics show that the Kuda peridotites occur in the abyssal mantle peridotite fields, and have lower CaO, Al₂O₃ and FeO^T contents than those in the primitive mantle. The mineralogical characteristics of the peridotites and geochemical signatures of the basalts indicate that the Kuda ophiolites have seen about 30% of partial melting of the peridotites, and recorded the tectonic transition from the mid-oceanic ridge to the subduction zone, similar to those of the Yarlung Zangbo suture zone.